incisive used in The Mill on the Floss

direct, clear, and sharp in thinking or expression — often indicating a decisive person (makes decisions quickly) or a penetrating mind

Philip was slow to reply, and when he spoke, his tone had a more incisive quietness and clearness than ever.

6.8 -- Book 6 Chapter 8 -- Wakem in a New Light (38% in)

"Miss Tulliver," he said, with bitter incisiveness, "has the only grounds of rank that anything but vulgar folly can suppose to belong to the middle class; she is thoroughly refined, and her friends, whatever else they may be, are respected for irreproachable honor and integrity.